The present invention relates to a new process for the production of N,O-disubstituted urethanes by reaction of N-monosubstituted or N,N'-disubstituted ureas or polyureas with dialkyl carbonates.
The production of lower molecular weight mono- or bis-urethanes, which may be split by the action of heat in a known manner into the isocyanate component thereof and the alcohol component thereof, is gaining in practical interest as a phosgene-free path to the corresponding isocyanates.
It has now surprisingly been found that it is possible to produce simple mono- or bis-urethanes which may be split by the action of heat into isocyanate and alcohol by reaction of N-substituted and, in particular, N,N'-disubstituted ureas with aliphatic carbonic esters. The reaction permits the production of the urethanes in particularly high yields when the catalysts described in detail below are also used.
The reaction according to the present invention is of particular practical interest because:
(a) the reaction between N,N'-disubstituted ureas and aliphatic carbonic esters takes place according to the following equation (wherein R and R' represent the inert radicals of the reactants): EQU R--NH--CO--NH--R+R'--O--CO--O--R'.fwdarw.2R--NH--CO--OR' PA1 (b) the substituted ureas or aliphatic carbonic esters to be used as starting materials are obtainable from inexpensive commercially available starting materials.
without the formation of by-products; and